Question

Prove that
Cos 510 Cos 330 + Sin 390 Cos 120 = -|
Step by step ​

Answer 1

$cos(540 - 30) \times cos(270 + 60) + sin(450 - 60) \times cos(90 + 30) \\ ( - cos30)(sin60) + (cos60)( - sin30) \\ - ((cos30 \: \times sin60) \: + (cos60 \: \times sin30)) \\ - (sin(30 + 60)) \\ - sin90 \\ - 1$